Aircraft generate high acoustic contamination levels, the engine being one of the greatest noise generators. In the case of reaction engines, these engines are protected by means of the cowling, reducing the noise considerably. This noise reduction is not only sought for the outside of the aircraft, but rather for protecting the passengers from the inconveniences during the trip.
In the case of propeller engines, the most common is that such engines are not protected by this cowl, therefore all the noise is transmitted through the air through the propagation of sound waves and through structural vibrations.
The noise generated by this type of engine located in the rear part of the aircraft is produced in several ways:                Direct acoustic noise: by means of the propagation of sound waves from the engine to the cabin through the air;        Indirect acoustic noise: by means of the propagation of sound waves from the engine through the covering of the tail-cone, subsequent propagation through the air and finally through the pressure bulkhead;        Direct structural noise: from the engine through the pylon and the fuselage structure of the aircraft.        Indirect structural noise: a direct acoustic noise from the engines to the covering of the tail-cone and subsequently through the structure of the tail-cone to the cabin.        
Studies carried out show that the noises which most affect the passenger cabin are indirect acoustic and indirect structural noise. The present invention will reduce the noise generated by both models.
In addition, aircraft with propeller engines use several noise dampening systems such as passive dampening systems (hydraulic and/or mechanical systems reducing the vibrations in the fixing of the engine in the structure of the aircraft), active dampening systems (microphone systems located throughout the airplane which register the vibrations of the propellers and emit in frequencies counteracting the vibrations) and thermal and acoustic insulating blankets which are arranged inside the covering. The drawback of these dampening systems described is that they involve a very high excess weight for the aircraft, at the same time also raising the costs given that they require a subsequent assembly in the aircraft.
The present invention solves the previous drawback.